During the testing of jet engines and in many other turbine and high pressure environments, it is often desirable to measure both static pressure (Ps) and dynamic pressure (Pd). The static pressure (Ps), in most instances, is usually very high (200 psi) and the dynamic pressure (Pd) is much lower. Accordingly, the dynamic pressure (Pd) may typically be twenty (20) times less than the static pressure (Ps). Additionally, the dynamic pressure (Pd) is also associated with a distinct frequency which occurs at a relatively high rate, for example five thousand (5,000) cycles per second or greater. To measure static pressure (Ps), one requires a transducer with a relatively thick diaphragm so that it can withstand the high static pressure (Ps). Thick diaphragms, however, have poor sensitivity to low pressures.
U.S. Pat. No. 6,642,594 (the “'594 patent”), entitled “SINGLE CHIP MULTIPLE RANGE PRESSURE TRANSDUCER DEVICE”, which issued on Nov. 4, 2003 to A. D. Kurtz, the inventor herein and is assigned to Kulite Semiconductor Products, Inc., the assignee herein, discloses problems with transducers designed to measure large pressures being utilized to measure low pressures. A pressure transducer adapted to measure relatively large pressures typically suffers from relatively poor resolution or sensitivity when measuring relatively low pressures because, as a span of the sensor increases, the resolution or sensitivity of that sensor at the ends of the span decreases.
Due to the properties of pressure sensors, it is extremely difficult to measure both static pressure (Ps) and dynamic pressure (Pd) unless one uses a thick diaphragm for high static pressure (Ps) in conjunction with a thin diaphragm for low dynamic pressure (Pd) fluctuations. However, a thin diaphragm will rupture when exposed to high static pressure (Ps). Such a thin diaphragm can be preserved by equalizing pressure on both sides of the diaphragm. However, if static (Ps) and dynamic pressures (Pd) are equal on both sides of the diaphragm, the sensor will be unable to make a pressure reading. If static pressure (Ps) is equal on both sides of the diaphragm, and dynamic pressure (Pd) is present only on one side, then the sensor will be able to accurately read the dynamic pressure (Pd) only. Therefore, there is need for a filter that can transmit high static pressure (Ps) to one side of a diaphragm while canceling out dynamic pressure (Pd).
U.S. Pat. No 6,642,594, entitled “SINGLE CHIP MULTIPLE RANGE PRESSURE TRANSDUCER DEVICE,” demonstrates that a low pressure sensor can be fabricated on the same chip as a high pressure sensor. Two sensors of differing pressure ranges are achieved by fabricating an enlarged diaphragm on the same chip as a smaller diaphragm both of the same thickness. The enlarged diaphragm sensor can measure the low, dynamic pressures (Pd), while the smaller diaphragm with identical thickness measures the high static pressure (Ps) in the environment. U.S. Pat. No. 7,057,247, entitled “COMBINED ABSOLUTE DIFFERENTIAL TRANSDUCER,” issued to A. D. Kurtz, the inventor herein, and assigned to Kulite Semiconductor Products, Inc., presents an absolute and differential pressure sensor fabricated on a single chip. The static and dynamic pressure sensors in accordance with embodiments of the present invention may combine both of these patents into a single chip that contains a high pressure, absolute sensor with a thick diaphragm to measure the large static pressures (Ps) and a low pressure, differential sensor with an enlarged diaphragm that is may be substantially the same thickness as that of the static sensor to measure the dynamic pressures (Pd). Through the use of a filter disclosed herein that passes the high static pressure (Ps) but attenuates the dynamic pressure (Pd), only the large static pressure (Ps) is transmitted to the backside of the differential, dynamic sensor's diaphragm. It is this filter that enables the dynamic sensor to measure solely the dynamic pressure (Pd) within the high pressure environment. U.S. Pat. No. 6,595,066, entitled “Stopped Leadless Differential Sensor,” issued to A. D. Kurtz, the inventor herein, and assigned to Kulite Semiconductor Products, Inc., presents a micro-machined structure referred to as a “stop” that prevents the dynamic sensor's diaphragm from deflecting beyond its elastic region, thereby preventing it from rupturing during the transience of the filter.